Book I. Propositions 27 and 28

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Angles AGH, GHD, and angles BGH, GHC.

1. b) Name the interior angles on the same side.

Angles AGH, GHC, and angles BGH, GHD.

1. c) Name the exterior angles on the same side.

Angles EGA, CHF, and angles EGB, FHD.

1. d) Name the angle which is on the same side and interior and
1. d) opposite to angle EGB; GHD;1. d)
to angle EGA; GHC;1. d)
to angle FHD; HGB.

2. When a straight line meets two straight lines, why is each pair of 2. alternate interior angles equal respectively to a pair of alternate 2. exterior angles? (Hence we may speak simply of the alternate
2. angles.)

Because they are vertical angles.

3. State the definition of parallel lines.

Parallel lines are straight lines that are in the same plane and do not meet, no matter how far extended in either direction.